Modular gland arrangements for a fluid end assembly

ABSTRACT

A closure element for a fluid end assembly that has two or more recessed grooves formed in its outer surface. The grooves are axially offset. A seal is placed in one and only one of the grooves. As wear occurs, the seal is relocated to one of the other grooves. Instead of a series of axially offset grooves in a single closure element, a kit may be formed from two or more otherwise identical closure elements, each with a single recessed groove at a different axial position. Another closure element has a series of ledge-like surfaces defining spaces within which a seal may be received. One outer surface surrounds one or more of the other surfaces. A seal is placed in one and only one of the spaces. As wear occurs, the seal is relocated to one of the other spaces.

SUMMARY

The present invention is directed to a kit comprising a fluid endassembly, a closure element, and at least one annular first seal. Thefluid end assembly comprises a housing having an external surface and aninternal chamber. A first conduit is formed in the housing that has afirst and a second section, each section independently interconnectingthe internal chamber and the external surface. A second conduit is alsoformed in the housing that intersects the first conduit andindependently interconnects the internal chamber and the externalsurface. The closure element comprises a body having at least twostructural features. Each structural feature comprises a pair ofexternal surfaces formed in an outer surface of the body. The externalsurfaces join at a first corner line and form two boundaries of arecessed space within which an annular seal is receivable. The annularfirst seal is positionable within the recessed space of any of thestructural features.

The present invention is also directed to a kit comprising a fluid endassembly, a first closure element, annular first seal, a second closureelement, and an annular second seal. The fluid end assembly comprises ahousing having an internal chamber and a conduit that intersects theinternal chamber and opens at a first surface of the housing. The firstclosure element comprises a body having a pair of external surfacesformed in an outer surface of the body. The external surfaces join at afirst corner line and form two boundaries of a recessed space withinwhich an annular seal is receivable. The annular first seal ispositioned within the recessed space of the first closure element. Thesecond closure element comprises a body having a pair of externalsurfaces formed in an outer surface of the body. The external surfacesjoin at a first corner line and form two boundaries of a recessed spacewithin which an annular seal is receivable. The recessed space of thesecond closure element is axially offset from the recessed space of thefirst closure element if those closure elements were superimposed. Theannular second seal is positioned within the recessed space of thesecond closure element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a fluid end assembly. The housing hasbeen partially cut away to better display installed closure elements.

FIG. 2 is a perspective view of a discharge cover from the fluid endassembly of FIG. 1.

FIG. 3 is a cross-sectional view of the discharge cover of FIG. 2,positioned within a conduit of a fluid end assembly.

FIG. 4 is a cross-sectional view of a sleeve positioned within a conduitof the fluid end assembly. A plunger is disposed within the sleeve.

FIG. 5 is a side elevation view of a second embodiment of a dischargecover.

FIG. 6 is a cross-sectional view of the discharge cover of FIG. 5,positioned within a conduit of a fluid end assembly.

FIG. 7 is a cross-sectional view of a second embodiment of a sleevepositioned within a conduit of a fluid end assembly. A plunger is showndisposed within the sleeve.

FIG. 8 is an exploded perspective view of components of the fluid endassembly. The discharge covers are those shown in FIG. 2, and thesleeves are those shown in FIG. 4.

FIG. 9 is an exploded perspective view of some of the components ofanother fluid end assembly. The discharge covers are those shown in FIG.5.

FIG. 10 is an exploded view of the fluid end assembly of FIG. 9, from adifferent perspective. The sleeves are those shown in FIG. 7.

FIG. 11 is a side elevation of a first discharge cover. Together withthe second and third discharge covers shown in FIGS. 12 and 13, it formsa kit of a third embodiment of discharge covers.

FIG. 12 is a side elevation view of a second discharge cover.

FIG. 13 is a side elevation view of a third discharge cover.

FIG. 14 is an exploded perspective view of some of the components ofanother fluid end assembly. The discharge covers are those shown inFIGS. 11-13.

FIG. 15 is an exploded view of the fluid end assembly of FIG. 14, from adifferent perspective.

DETAILED DESCRIPTION

Fluid end assemblies are typically used in oil and gas operations todeliver highly pressurized corrosive and/or abrasive fluids to pipingleading to the wellbore. The assemblies are typically attached to powerends run by engines. The power ends reciprocate plungers within theassemblies to pump fluid throughout the fluid end. Fluid may be pumpedthrough the fluid end at pressures that range from 5,000-15,000 poundsper square inch (psi). Fluid used in high pressure hydraulic fracturingoperations is typically pumped through the fluid end at a minimum of8,000 psi; however, fluid will normally be pumped through the fluid endat pressures around 10,000-15,000 psi during such operations.

With reference now to FIG. 1, a fluid end assembly 10 comprising ahousing 12 having an external surface 14 and an internal chamber 16 isshown. A first conduit 18 and a second conduit 20 are formed within thehousing 12. The conduits 18 and 20 intersect each other to form theinternal chamber 16. As shown in FIG. 1, the diameter of the conduits 18and 20 may vary throughout the housing 12. This allows the conduits 18and 20 to closely receive structures of different sizes described laterherein.

The first conduit 18 shown in FIG. 1 has aligned first and secondsections 22 and 24, and the second conduit 20 has aligned third andfourth sections 26 and 28. Each section 22, 24, 26, and 28 independentlyconnects the internal chamber 16 and the external surface 14. Thesections 22, 24, 26, and 28 are aligned such that the conduits 18 and 20are orthogonal to one another. However, the sections 22, 24, 26, and 28may also be aligned so they intersect the internal chamber 16 at anon-straight angle.

In another embodiment, the second conduit 20 may only comprise a thirdsection 26, meaning the second conduit 20 only has one opening on theexternal surface 14. The fourth section 28 is not required for operationof the fluid end 10. The fourth section 28 is typically machined in thehousing 12 for ease of creating the second conduit 20 and to provide anopening to service parts within the housing 12, if needed.

The second section 24 has an intake opening 68. The intake opening 68may be secured to a piping system that delivers fluid to the fluid end10. A set of valves 70 and 72 are positioned within the first conduit18. The valves 70 and 72 help move fluid within the housing 12. Anintake valve 72 prevents fluid from flowing back through the intakeopening 68 after entering the housing 12. A discharge valve 70 allowsfluid to exit the fluid end 10 through a discharge opening 74 positionedproximate a top end 76 of the fluid end 10. Each of the valves 70, 72may also have a seal 78 positioned around its outer surface to blockfluid from leaking around the valves 70, 72.

With reference to FIGS. 1 and 8, the housing 12 may have a plurality offirst and second conduits 18 and 20 positioned adjacent one another.Each first conduit 18 may have an intake opening 68 formed in its secondsection 24. The intake openings 68 may each be connected to a differentcoupler or pipe that leads to the same piping system (not shown). Thisallows fluid to enter the fluid end 10 through multiple openings. Incontrast, only one discharge opening 74 may be formed in the housing 12.Each first section 22 of the first conduits 18 may be connected to thedischarge opening 74. This allows fluid to exit the housing 12 through asingle opening.

A second discharge opening (not shown) may also be formed in the housing12 that is in fluid communication with the discharge opening 74. Thisallows fluid to exit the housing 12 through two openings. Additionaldischarge openings may also be formed in the housing 12, if needed.

With reference to FIG. 1, a plurality of closure elements 30, 32, and 34are shown positioned within the first, third, and fourth sections 22,26, and 28. The closure element positioned within the first section 22is a discharge cover or discharge plug 30, and the closure elementpositioned within the fourth section 28 is a suction cover or suctionplug 32. The covers 30 and 32 are substantially identical. Each cover30, 32 is sized to fully block fluid flow within the section 22 or 28 itis situated in. The covers 30 and 32 are retained within each section 22or 28 by a retaining nut 36 that threads into each section 22 and 28proximate the external surface 14 of the housing 12.

The closure element positioned within the third section 26 is a sleeve34. The sleeve 34 is tubular and sized to be closely received within thethird section 26. The sleeve 34 is retained within the third section 26by a tubular retaining nut 40. The retaining nut 40 threads into thethird section 26 proximate the external surface 14 of the housing 12.

A plunger 42 is shown disposed within the sleeve 34 and the retainingnut 40. During operation, the plunger 42 reciprocates within the housing12 to pump fluid throughout the fluid end 10. The plunger 42 is poweredby a power end run by an engine (not shown) that is connected to a firstend 44 of the plunger 42.

Each of the closure elements 30, 32, and 34 has a seal 46 positionedaround its outer surface to block fluid from leaking from the sections22, 26, or 28. The seals 46 block the flow of fluid by tightly engagingan inner surface or sealing surface 48 of conduits 18 and 20.

Fluid end assemblies 10 are susceptible to corrosive and/or abrasivefluid becoming trapped between the seal 46 and the sealing surface 48.This may cause the sealing surfaces 48 to erode over time and preventthe seals 46 from tightly engaging the sealing surfaces 48. Fluid mayleak from the sections 22, 26, and 28 if the seals 46 cannot effectivelyseal against the sealing surfaces 48. If fluid leaks from the fluid end10, the housing 12 will likely need to be replaced, because it may nolonger maintain the requisite fluid pressure for operation.

The present invention is directed to a system including one or moreclosure elements 30, 32, and 34 that permit the seal 46 to be relocatedwithin the conduits 18 and 20 over time. Relocating the seal 46 alsorelocates the sealing surface 48. Thus, if the original sealing surface48 suffers erosion, the seal 46 can be moved to engage with a differentsealing surface 48 in the conduits 18 or 20. Such relocation will helpextend the life of the fluid end housing 12.

Turning now to FIG. 2, a first embodiment of the closure element 100 isshown. A discharge cover 30 is shown in FIG. 2, but a suction cover 32or a sleeve 34 may also be used with the closure element 100 (FIGS. 4and 8). The closure element 100 comprises a body 102 having a topsurface 104, a bottom surface 106 and an outer surface 108.

The body 102 further comprises a plurality of structural features makingup a first recessed space 110, a second recessed space 112, and thirdrecessed space 114. The recessed spaces 110, 112, and 114 are eachformed by paired external surfaces 116 and 118 that join at a firstcorner line 120 and form a ledge at an outer edge of the body 102. Theexternal surfaces 116 and 118 form the boundaries of each recessed space110, 112, and 114. An annular seal 122 is positionable within one of therecessed spaces 110, 112, and 114 (FIGS. 3 and 4).

The first recessed space 110 has a larger circumference than the secondrecessed space 112, and the second recessed space 112 has a largercircumference than the third recessed space 114. The structural featuresmaking up the recessed spaces 110, 112, and 114 shown in FIG. 2 followsubstantially the same path around the outer surface 108 of the body102. However, the recessed spaces 110, 112, and 114 may followdifferently shaped paths around the outer surface 108 of the body 102,if desired.

With reference now to FIGS. 3 and 4, the closure elements 100 are shownpositioned within the conduits 18 and 20. The discharge cover 30 isshown in FIG. 3 and the sleeve 34 is shown in FIG. 4. The closureelements 100 are positioned within the sections 22 or 28 such that thebottom surface 106 faces towards the internal chamber 16 (FIG. 1). Theretaining nut 36 or 40 is positioned above the top surface 104 of theclosure element 100. As shown in FIG. 4, the sleeve 34 is hollow in thecenter to make room for the plunger 42. A packing seal or series ofpacking seals 50 may also be positioned inside of the sleeve 34 to blockfluid from leaking between the sleeve 34 and the plunger 42.

Continuing with FIGS. 3 and 4, the sealing surface 48 for each seal 122comprises paired surfaces formed in the internal walls of the conduits18 or 20. The paired surfaces correspond with the recessed spaces 110,112, and 114 formed in the closure element 100. Thus, the inner walls ofthe conduits 18 or 20 further bound the recessed spaces 110, 112, and114 to tightly engage the seal 122.

Turning now to FIG. 5, a second embodiment of the closure element 200 isshown. A discharge cover 30 is shown in FIG. 5, but a suction cover 32or a sleeve 34 may also be used with the closure element 200 (FIGS. 7,9, and 10). The closure element 200 comprises a body 202 having a topsurface 204, a bottom surface 206 and an outer surface 208.

A plurality of structural features are formed in the body 202 that makeup a first recessed space 210, a second recessed space 212, and thirdrecessed space 214. The recessed spaces 210, 212, and 214 are eachformed by paired external surfaces 216 and 218 that join at a firstcorner line 220 and form a ledge at an outer edge of the body 202. Therecessed spaces 210, 212, and 214 are further bounded by a thirdexternal surface 222 of the body 202 that joins one of the pairedexternal surfaces 216, 218 at a second corner line 224. The threeexternal surfaces 216, 218, and 222 together form a groove in the body202.

The recessed spaces 210, 212, and 214 are axially spaced on the outersurface 208 of the body 202 and are substantially identical in shape andsize. However, the spaces 210, 212, and 214 may vary in size and shape,if desired. An annular seal 226 is positionable within one of therecessed spaces 210, 212, and 214 (FIGS. 6 and 7).

With reference now to FIGS. 6 and 7, the closure elements 200 are shownpositioned within the conduits 18 and 20. The discharge cover 30 isshown in FIG. 6 and the sleeve 34 is shown in FIG. 7. The closureelements 200 are positioned within the sections 22 or 28 such that thebottom surface 206 faces towards the internal chamber 16 (FIG. 1). Theretaining nut 36 or 40 is positioned above the top surface 204 of theclosure element 200. As shown in FIG. 7, the sleeve 34 is hollow in thecenter to make room for the plunger 42. Like closure element 100, apacking seal or series of packing seals 228 may also be positionedinside of the sleeve 34 to block fluid from leaking between the sleeve34 and the plunger 42.

Continuing with FIGS. 6 and 7, the sealing surface 48 for each seal 226is the area of the internal wall of the conduit 18 or 20 that tightlyengages the seal 226. This area is typically the portion of the internalwall directly across from the position of the seal 226, when the closureelement 200 is positioned within the conduits 18 or 20.

Turning now to FIGS. 8-10, the first and second embodiments of theclosure elements 100 and 200 may be utilized in the same manner. Inoperation, an operator will put a first seal 122A or 226A in the firstrecessed space 110 or 210 and leave the second and third recessed spaces112, 212, 114, and 214 empty (FIGS. 2 and 5). The operator will theninstall the closure element 100 or 200 into one of the conduits 18 or 20and secure it with the retaining nut 36 or 40.

The power end attached to the fluid end 10 is then activated such thatfluid begins to flow throughout the fluid end 10. During operation, thesealing surface 48 within the conduit 18 or 20 will start to erode. Ifthe seal 122A or 226A starts to leak, the power end is deactivated tostop fluid flow. The closure element 100 or 200 is removed from theconduit 18 or 20 and the first seal 122A or 226A is removed from thefirst recessed space 110 or 210 (FIGS. 2 and 5).

A second seal 122B or 226B is positioned within the second recessedspace 112 or 212 leaving the first and third recessed spaces 110, 210,114, and 214 empty (FIGS. 2 and 5). The closure element 100 or 200 isinstalled into the same conduit 18 or 20 it was removed from andoperations may resume. Because the position of the second seal 122B or226B is axially spaced from that of the first seal 122A or 226A, thesecond seal 122B or 226B will have a new non-eroded sealing surface 48on the internal surface of the conduit 18 or 20 (FIGS. 3, 4, 6 and 7).Thus, the second seal 122B or 226B will offer enhanced resistance fromleakage from the conduit 18 or 20.

As the sealing surfaces 48 experience erosion, the seal 122B or 226B maybegin to leak. In such case, the power end is again deactivated and theclosure element 100 or 200 is removed from the conduit 18 or 20, and thesecond seal 122B or 226B is removed from the second recessed space 112or 212. A third seal 122C or 226C is positioned within the thirdrecessed space 114 or 214 leaving the first and second recessed spaces110, 210, 112, and 212 empty (FIGS. 2 and 5). The closure element 100 or200 is again installed into the conduit 18 or 20 and operations mayresume. Because the position of the third seal 122C or 226C is axiallyspaced from that of the first and second seal 122A, 122B, 226A, and226B, the third seal 122C or 226C will have a new non-eroded sealingsurface 48 (FIGS. 3, 4, 6, and 7). Thus, the third seal 122C or 226Cwill offer enhanced resistance from leakage from the conduit 18 or 20.

The operator may choose any order of positioning the seals within thegrooves desired. The order of operation described above is non-limitingand is just one method of using the closure elements 100 or 200. Forexample, the operator may start by positioning the third seal 122C or226C in the third recessed spaces 114 or 214, rather than starting bypositioning the first seal 122A or 226A in the first recessed spaces 110or 210.

The same methods described above may be employed using a closure element100 or 200 having only two recessed spaces or having more than threerecessed spaces. Once the final seal no longer seals properly againstits sealing surface 48, the fluid end housing 12 will likely need to bereplaced.

In operation, this method is employed for each conduit 18 or 20individually. FIGS. 8-10 show the seals 122A, 122B, 122C, 226A, 226B,and 226C positioned within a different recessed space 110, 112, 114,210, 212, and 214 (FIGS. 2 and 5) in each type of closure element 100and 200 for illustrative purposes only. In reality, each closure element100 or 200 starts with the first seal 122A or 226A in the first recessedspace 110 or 210. The first seal 122A or 226A may be removed and thesecond seal 122B or 226B is placed in the second recessed space 112 or212, and so on, only when necessary for each closure element 100 or 200.

Turning now to FIGS. 11-13, a third embodiment of the closure element300 is shown. The closure element 300 utilizes a kit comprising multipleclosure elements 302, 304, and 306. Discharge covers 30 are shown inFIGS. 11-13, but suction covers 32 or sleeves 34 may also be used withthe closure element 300 (FIGS. 14 and 15).

The kit making up the closure element 300 includes a first closureelement 302, a second closure element 304, and third closure element306. Except as described hereafter, the closure elements 302, 304, and306 are identical in size and shape to closure elements 200. Eachclosure element 302, 304, and 306 has a single structural feature formedin the outer surface of its body 314 in the form of a recessed space308, 310, and 312. The recessed spaces 308, 310, and 312 are configuredidentically to the recessed spaces 210, 212, and 214 formed in thesecond embodiment of the closure element 200 (FIG. 5).

The first closure element 302 has a first recessed space 308 formedproximate a top surface 316 of its body 314. The second closure element304 has a second recessed space 310 formed proximate the center of thebody 314, and the third closure element 306 has a third recessed space312 formed proximate a bottom surface 318 of its body 314. Thus, therecessed spaces 308, 310, and 312 are axially offset from one another ifthe closure elements 302, 304, and 306 are superimposed. A first,second, and third seal 320A, 320B, and 320C may be positioned withineach corresponding recessed space 308, 310, and 312 (FIGS. 14 and 15).

Turning now to FIGS. 14 and 15, in operation, the operator will installthe first closure element 302 into one of the conduits 18 or 20 andsecure it with the retaining nut 36 or 40. The power end attached to thefluid end 10 is activated such that fluid begins to flow throughout thefluid end 10. Over time, the sealing surface 48 of the first seal 320Awill start to erode. If the first seal 320A starts to leak, the powerend is deactivated to stop fluid flow. The first closure element 302 isremoved from the conduit 18 or 20 and replaced with the second closureelement 304.

Because the position of the second seal 320B on the second closureelement 304 is axially spaced from that of the first seal 320A on thefirst closure element 302, the second seal 320B will have a newnon-eroded sealing surface 48 in the conduit 18 or 20. Thus, the secondseal 320B will offer enhanced resistance from leakage from the conduit18 or 20.

As the sealing surfaces 48 experience erosion, the second seal 320B maybegin to leak. In such case, the power end is again deactivated and thesecond closure element 304 is removed from the conduit 18 or 20 andreplaced with the third closure element 306. Because the position of thethird seal 320C on the third closure element 306 is axially spaced fromthe first and second seals 320A and 320B on the first and second closureelements 302 and 304, the third seal 320C will have a new non-erodedsealing surface 48. Thus, the third seal 320C will offer enhancedresistance from leakage from the conduit 18 or 20.

The operator may choose any order of positioning the closure element302, 304, and 306 within the conduits 18 or 20 desired. The order ofoperation described above is non-limiting and is just one method ofusing the kit making up the closure element 300. For example, theoperator may start by positioning the third closure element 306 in theconduit 18 or 20, rather than starting by positioning the first closureelement 302 in the conduit 18 or 20.

This same method may be employed using only two different closureelements 300 or more than three different closure elements 300. Once theseal on the final closure element no longer seals properly, the fluidend housing 12 will likely need to be replaced.

This same method may also be employed using the first embodiment 100 ofthe closure element 100. In such case, each closure element would onlyhave one recessed space formed in its body that is identical to therecessed spaces 110, 112, or 114 shown in FIG. 2. The recessed spaceswould be axially offset if those closure elements were superimposed.

In operation, this method is employed for each conduit section 22, 26,or 28 (FIG. 1) individually. FIGS. 14 and 15 show a different closureelement 302, 304, or 306 positioned within each conduit section 22, 26,or 28 for illustrative purposes only. In reality, each conduit section22, 26, or 28 would start with the first closure element 302. The firstclosure element 302 would be removed and replaced with the secondclosure element 304, and so on, only when necessary for each conduitsection 22, 26, or 28.

Turning back to FIG. 1, the seals 78 on the valves 70, 72 may have thesame problems as the seals 46 used on the closure elements 30. Due tothis, the embodiments 100, 200, and 300 and methods discussed above mayalso be employed on the valves 70 and 72.

Various modifications can be made in the design and operation of thepresent invention without departing from the spirit thereof. Thus, whilethe principle preferred construction and modes of operation of theinvention have been explained in what is now considered to represent itsbest embodiments, which have been illustrated and described, it shouldbe understood that the invention may be practiced otherwise than asspecifically illustrated and described.

The invention claimed is:
 1. A fluid end assembly, comprising: a housinghaving an external surface, an internal chamber, and at least twoconduits independently interconnecting the external surface and theinternal chamber; a closure element received within one of the conduitsand comprising: a body having at least two axially spaced andcircumferential grooves formed therein; and one and only one annularseal, the seal positioned within one of the grooves of the body.
 2. Thefluid end assembly of claim 1 in which the closure element is a plugsized to be closely received within the conduit.
 3. The fluid endassembly of claim 1 in which the closure element is a tubular sleevesized to be closely received within the conduit.
 4. The fluid endassembly of claim 3, further comprising: a plunger disposed at leastpartially within the tubular sleeve.
 5. The fluid end assembly of claim1 in which the circumferential groove comprises two sidewalls joined bya base.
 6. A fluid end kit, comprising: a housing having an externalsurface, an internal chamber, and at least two conduits independentlyinterconnecting the external surface and the internal chamber; a closureelement receivable within one of the conduits and comprising: a bodyhaving a stairstep profile, the stairstep profile being formed by atleast two axially spaced and circumferential structural features; and atleast one annular seal, the seal positionable around any of thestructural features.
 7. The fluid end kit of claim 6 in which theclosure element is a plug sized to be closely received within theconduit.
 8. The fluid end kit of claim 6 in which the closure element isa tubular sleeve sized to be closely received within the conduit.
 9. Thefluid end kit of claim 6 in which the at least two structural featuresinclude first and second structural features, and an axial footprint ofthe first structural feature fully surrounds an axial footprint of thesecond structural feature.
 10. The fluid end kit of claim 6 in which theat least two structural features each comprise: a pair of externalsurfaces formed in an outer surface of the body, the external surfacesjoining at a first corner line and forming two boundaries of a recessedspace within which an annular seal is receivable.
 11. A fluid end kit,comprising: a housing having an external surface, an internal chamber,and at least two conduits independently interconnecting the externalsurface and the internal chamber; a first closure element receivablewithin at least one of the conduits and comprising a body having one andonly one circumferential recess formed therein; a second closure elementreceivable within one of the conduits as the first closure element andcomprising a body having one and only one circumferential recess formedtherein; and at least one annular seal positionable in the recess formedin the first or second closure element; in which the respective recesseswould be axially setoff if the first and second closure elements weresuperimposed.
 12. The fluid end assembly of claim 11 in which theclosure element is a plug sized to be closely received within theconduit.
 13. The fluid end assembly of claim 11 in which the closureelement is a tubular sleeve sized to be closely received within theconduit.
 14. The fluid end assembly of claim 13, further comprising: aplunger disposed at least partially within the tubular sleeve.
 15. Thefluid end assembly of claim 11 in which the circumferential groovecomprises two sidewalls joined by a base.
 16. A system, comprising: thekit of claim 11, in which the first closure element is positioned withinone of the conduits, and the at least one annular seal is positioned inthe one and only one circumferential recess; high pressure fluidpositioned within at least a portion of the housing; and the secondclosure element positioned outside of the housing.
 17. A fluid end kit,comprising: a housing having an external surface, an internal chamber,and at least two conduits independently interconnecting the externalsurface and the internal chamber; a closure element receivable withinone of the conduits and comprising: a body having at least twoaxially-spaced circumferential recesses formed in its external surface,each recess following a path having an axial footprint, the axialfootprint of one of the recesses wholly surrounding the axial footprintof another one of the recesses; and at least one annular seal, the sealpositionable within one of the recesses.
 18. The fluid end assembly ofclaim 17 in which the closure element is a plug sized to be closelyreceived within the conduit.
 19. The fluid end assembly of claim 17 inwhich the closure element is a tubular sleeve sized to be closelyreceived within the conduit.
 20. The fluid end assembly of claim 19,further comprising: a plunger disposed at least partially within thetubular sleeve.